A knight in shining armor turned out to be a wolf in sheep’s clothing Saturday when a man rushed over to a woman who had just slipped on ice — and robbed her, authorities said.

The 23-year-old woman had just stepped out of a building on East 15th Street near Union Square at around 3:30 a.m. before taking a spill on a patch of ice, cops said.

A man who happened to be standing nearby came running over in a seeming attempt to assist the damsel in distress, helping her get to her feet.

But just as the woman was about to thank the no-good “do-gooder,” the man barked, “Give me what you have” — before reaching into her pocket and stealing $50 in cash, a MetroCard and her ID, according to police.

The disingenuous thief, whom cops described as a male in his 30s standing around 5-foot-10 and weighing about 180 pounds, ran down the block before bolting north on Broadway.